Olefins such as ethylene and propylene have a wide variety of uses. Examples include isomerization and oligomerization to fuel products, and polymerization to plastic products. In many cases, the olefins which are to be further used as a feed stream also contain contaminants such as oxygenates which must be substantially removed.
For example, U.S. Pat. No. 6,403,854 (Miller et al.) discloses removal of an oxygenate contaminant such as dimethyl ether from an olefin stream made by contacting methanol with a silicoaluminophosphate (SAPO) catalyst. The oxygenate contaminant is removed by cooling the olefin stream in a two stage quench process. In the first stage of the process, a substantial portion of the dimethyl ether is removed along with condensed water as a bottoms product. Additional dimethyl ether is removed in the second stage, and the olefin overhead is further treated for oxygenate removal by contacting with an adsorbent.
EP 0 229 994 (Union Carbide Corp.) discloses the removal of dimethyl ether from a liquid C3-C5 olefin. More specifically, the liquid olefin contains from 5 to 50 weight percent monoolefins having from 3 to 5 carbons, from 100 to 20,000 ppm by weight diolefins, and from 1 to 5,000 ppm by weight dimethyl ether, in liquid state through an adsorbent mass of a crystalline zeolite molecular sieve. The zeolite has a faujasite structure, and includes zeolite Y, zeolite X, and zeolite LZ-210. Preferably, the olefin stream is a mixed C4-C5 hydrocarbon stream and comes from a fluid catalytic cracking (FCC) unit, with the bulk of the isobutylene and/or isoamylene content in the olefin having been removed by reacting the olefin FCC product with methanol to form MTBE or TAME. The adsorption system can be a fixed bed, moving bed, simulated moving bed or fluidized bed system, but is preferably a fixed bed system.
Conventional processes for removing oxygenates such as dimethyl ether or acetaldehyde from an olefin stream are complex, provide insufficient removal of the oxygenate or convert a significant percent of the olefin product to undesirable by-products such as olefin oligomers. Therefore, additional processes are desired.